The general field of the invention relates to microwave feed apparatus for a common cavity microwave and electric self-clean oven. More particularly, the invention relates to a backfed common cavity microwave and electric oven.
Heating uniformity has been a primary consideration throughout the development of microwave ovens. In first generation microwave ovens, the microwave energy was either excited in the cavity by the direct insertion of the magnetron probe or the microwave energy was coupled to a waveguide that communicated with the cavity. In either case, complex standing waves were set up in the cavity causing "hot" spots. To improve heating uniformity, mode stirrers or moving metal parts were introduced into the cavity so that the complex standing wave patterns and hence hot spots moved.
Later, radiating antennas or primary radiators were introduced and their objective was to provide a directive uniform radiated pattern so that a larger percentage of the microwave energy would be transmitted directly to the food rather than reflecting off the walls where standing waves and hot spots could be set up. It was recognized that the heating uniformity of primary radiators could be enhanced by rotating them. Still another technique for improving heating uniformity was the introduction of a turntable that moved the food relative to the microwave radiated pattern.
The heating uniformity within a food body is also a function of the geometry of the food body. For example, one common food body geometry is horizontally large but vertically short such as a snacking cake or a casserole in a low, flat dish. For this common geometry, it has generally been felt that it is necessary to feed the microwave energy into the cavity from either the top or bottom, and this is especially true when a directive radiating antenna is used. Accordingly, the microwave energy entering either the top or bottom large surface is relatively uniform so that the entire body heats at approximately the same rate. It has also been felt and demonstrated that if the microwave energy were directed at such a geometry from the side, the depth of penetration would generally be such that the side facing the source would absorb most of the available microwave energy thereby heating it rapidly while the opposite side remained relatively cool or underdone.
As a result of the above, microwave ovens including common cavity microwave and electric ovens with directive antennas have generally been fed from either the top or bottom of the cavity. The top mounting has the disadvantage that the temperature of the microwave components becomes quite hot during self-cleaning. The bottom feed has the disadvantage in that provisions generally must be taken to prevent oven spills from running into an open waveguide. Further, with a common cavity wall oven, there is physically very little room for the microwave apparatus at the top and bottom of the cavity.